In recent years, intensive studies have been made on how to manufacture three-dimensional optical integrated circuits of a waveguide, an optical branching circuit, a directional coupler, and the like inside glass. Those methods for manufacturing such optical integrated circuits may include one that employs femtosecond laser light. For example, this method induces an impact at the light condensing point of the femtosecond laser light due to the two-photon absorption or the like, whereby the refractive index of the glass can be locally changed. Further, such light condensing irradiation of laser light onto an irradiation object has been widely employed not only for manufacturing the optical integrated circuit but also for various laser processing devices or laser microscopes by which scattering and reflection of laser light are observed (for example, refer to Patent Documents 1 to 3, Non-Patent Documents 1 to 6).
Here, in the case where one laser light beam emitted from a laser light source may be used for laser light irradiation to process a complicated three-dimensional structure, etc., this processing step would require an enormous amount of time. To reduce the processing time for this case, it can be thought to employ a plurality of light condensing points for multispot simultaneous processing. The simplest configuration for achieving such a method is to employ a plurality of laser light beams that are supplied from a plurality of laser light sources. However, such a configuration is not realistic when costs for preparing and space for mounting a plurality of laser light sources are taken into consideration.
In contrast to this, studies have been made for a method for achieving the multispot simultaneous processing using a phase-modulation type spatial light modulator (SLM: Spatial Light Modulator) and a hologram (CGH: Computer Generated Hologram) determined by numerical calculation. When laser light is input to the spatial light modulator with a CGH presented therein, the phase of the input light is modulated depending on the modulation pattern of the CGH. Then, when the wavefront of the modulated laser light output from the light modulator is condensed by the Fourier transform lens, it is possible to produce a plurality of light condensing points from one laser light beam, thereby enabling laser operations such as simultaneous processing and simultaneous observations by a multispot simultaneous irradiation.
In the multispot simultaneous processing inside an irradiation object (a processing object) using the spatial light modulator, it is possible to condense laser light at any position in one plane perpendicular to the optical axis. Further, in such multispot simultaneous processing, for example, a method may be employed in which a Fresnel lens pattern having the lens effect is presented in the spatial light modulator, thereby enabling the laser light to be condensed at an arbitrary three-dimensional position including the direction of the optical axis.